Behavior Of Steel Fiber Reinforced Concrete Research Articles

Effect of fresh concrete compression technique on pre- and post-heating compressive behavior of steel fiber-reinforced concrete: Experiments and RSM-based optimization

Despite the many advantages of fresh concrete compression technique for improving the performance of hardened concrete under compression, no study has so far addressed various behavioral aspects of this type of concrete in different conditions and scenarios such as fire, which may occur during the service life for a structure made up of this concrete type. Here, the compressive performance of compressed concrete with steel fibers was addressed before and after experiencing elevated temperatures considering key variables including the volume quantity of steel fibers, diameter-to-thickness ratio of steel tube (mold), capacity of the reference concrete, and exposure temperature. To reach this goal, 60 concrete cylinders were tested under axial compression, and the results including the compressive strength, elastic modulus, strain at peak stress, toughness, axial stress–strain graph, and weight loss were assessed together with the results of a visual inspection, failure mode, and microstructure of concrete. The results demonstrated that although the fresh concrete compression technique notably improved the mechanical features of concrete, especially the compressive strength by up to 100 % at the ambient temperature, adding steel fibers, lowering the water-to-cement ratio (w/c), and using a tube with a thinner wall as the mold lowered the efficiency of this technique in improving the compressive performance. In addition, the amount of increase in concrete strength due to compressing the fresh concrete had a linear relationship with the amount of excess water removed from it. The positive impact of the fresh concrete compression technique on the concrete strength at high temperatures was significant. In this regard, the compressive strength reduction of the compressed concrete was 20 % lower than that of the uncompressed concrete. However, the fresh concrete compression technique was not very effective against the deterioration of the modulus of elasticity caused by high temperatures. Ultimately, the response surface method (RSM) was used to reach an optimum solution for the design variables that could maximize the compressive capacity of fibrous compressed concrete per different target temperatures.

Serviceability evaluation model of SFRC beams reinforced with FRP bars based on deformation control

This research investigated the flexural behavior of steel fiber-reinforced concrete (SFRC) beams reinforced with fiber-reinforced polymer (FRP) bars to promote its application in engineering. Ten beams with widths of 150 mm, heights of 250 mm and lengths of 1800 mm were tested under four-point bending. The experimental parameters included the reinforcement type, steel fiber volume fraction, concrete strength, and longitudinal reinforcement ratio of the FRP bars. Based on the test results, a prediction model was proposed for the balanced reinforcement ratio (ρfb), considering the influence of steel fibers. Deformation prediction equations in the current design codes in the US, China, and Canada were compared based on the experimental results. The increase in the reinforcement ratio (ρf) can improve both the service moment (Ms) and the ultimate moment (Mu). With an increase in ρf/ρfb, the Ms/Mu value decreased for under-reinforcement beams but increased for over-reinforcement beams. Based on the linear regression theory, a new calculation model for the flexural moment utilization efficiency of SFRC beams reinforced with FRP bars in serviceability limit states is established. The ductility indices of all beams are above the minimum limit of 4, as proposed by CSA S6-14.

Experimental and MCFT-Based Study on Steel Fiber-Reinforced Concrete Subjected to In-Plane Shear Forces

Testing of concrete panels subjected to pure in-plane shear loading is necessary to elucidate the shear behavior of concrete. However, available data for predicting the shear capacity and behavior of steel fiber-reinforced concrete are rather limited. This study aims to evaluate the shear capacity and behavior of fiber-reinforced concrete made of highly flowable strain hardening fiber-reinforced concrete (HF-SHFRC) experimentally and analytically, respectively, using a panel tester loaded under pure shear and modified compression field theory (MCFT). The test was conducted using a panel test machine at the University of Toronto. The test results of the HF-SHFRC demonstrated strain hardening behavior at tension after the first crack, as indicated by the increase in the shear stress after the first crack in the HF-SHFRC panel. An analysis procedure is proposed for predicting the shear strength of steel fiber-reinforced concrete (SFRC) based on experimental data of the SFRC panels to obtain reliable results. A comparison of results obtained from the proposed analysis procedure and experiments show that it accurately predicted the response of the HF-SHFRC. The proposed MCFT-based analysis procedure can provide valuable insight for understanding the behavior of the SFRC panels under shear loading.

An Experimental Approach for the Study on Mechanical Properties of M30 Grade Concrete when the Steel Fibers are Induced

Abstract: Fibre Reinforced Concrete (FRC) material is a developed concrete that has been proposed to improve the tensile behaviour of the concrete using fibres in the concrete mix. Steel Fibre Reinforced Concrete (SFRC) is popular FRC material that is being studied to improve the structural behaviour of members under different load conditions. This study aims to investigate and examine the structural behaviour of steel fibre reinforced concrete material at different volume fraction of the fibers. Experimental work is conducted for this research to obtain results on the behaviour of SFRC. The experimental work consists of testing concrete under tension and compression. A result data obtained has been analyzed and compared with a control specimen (0% fiber).a relationship between aspect ratio Vs compressive strength, aspect ratio Vs spilt tensile strength represented graphically. Result data clearly shows percentage increase in 28 days compressive strength and spilt tensile strength for M30 Grade of concrete.

Compressive behavior of steel-fiber reinforced concrete in Annex L of new Eurocode 2

This paper describes the model for the compressive stress-strain behavior of steel fiber-reinforced concrete (SFRC) in Annex L of the new Eurocode 2 (version 2022-05, EC2), developed within CEN TC250/SC2/WG1/TG2 – Fiber reinforced concrete. The model uses functions obtained from correlations with an extensive database comprised of 197 well-documented SFRC compressive tests and 484 flexural tests. We detailedly explain the model and derive the strain values for the parabola-rectangle model for ULS of SFRC in Annex L. In addition, we also use the model and the correlations with the database to provide a link between the compressive and the flexural performance classes in EC2, which allows a complete definition of any particular SFRC. Likewise, we derive parabola-rectangle strain values for each flexural performance class, which is mainly advantageous for the stronger flexural classes. Finally, we give an example showing the enhancement in strength and ductility of a composite steel-SFRC section endorsed with the new model, which results of 15% and 100%, respectively.

Evaluation of the Tensile Characteristics and Bond Behaviour of Steel Fibre-Reinforced Concrete: An Overview

Conventional concrete is a common building material that is often ridden with cracks due to its low tensile strength. Moreover, it has relatively low shear strength and, unless reinforced, undergoes brittle failure under tension and shear. Thus, concrete must be adequately reinforced to prevent brittle tensile and shear failures. Steel fibres are commonly used for this purpose, which can partially or fully replace traditional steel reinforcement. The strength properties and bond characteristics between reinforcing steel fibres and the concrete matrix are crucial in ensuring the effective performance of the composite material. In particular, the quality of the bond has a significant impact on crack development, crack spacing, and crack width, among other parameters. Hence, the proper application of steel fibre-reinforced concrete (SFRC) requires a thorough understanding of the factors influencing its bond behaviour and strength properties. This paper offers a comprehensive review of the main factors controlling the bond behaviour between concrete and steel fibres in SFRC. In particular, we focus on the effects of the physical and mechanical properties of steel fibres (e.g., geometry, inclination angle, embedded length, diameter, and tensile strength) on the bond behaviour. We find that the addition of up to 2% of steel fibres into concrete mixtures can significantly enhance the compressive strength, tensile strength, and flexural strength of concrete components (by about 20%, 143%, and 167%, respectively). Furthermore, a significant enhancement in the pull-out performance of the concrete is observed with the addition of steel fibres at various dosages and geometries.

Effect of interfacial transition zone on creep behavior of steel fiber-reinforced concrete

• A SFRC creep prediction model considering ITZ was established. • The role of ITZ in SFRC was revealed. • The effects of relevant factors on SFRC creep were analyzed. • The key factors affecting SFRC creep were determined. To explore the interface transition zone (ITZ) effect on the creep behavior of steel fiber-reinforced concrete (SFRC), this study proposed a three-phase creep prediction model based on the mesomechanical shear lag theory. The model verification was performed using available creep data, and three influencing factors were analyzed. The proposed creep prediction model well described the creep behavior of SFRC, revealing the ITZ's role in it. The specific creep values of SFRC at the loading age of 365d with 1, 2, and 3% steel fiber contents exceeded those assessed without the ITZ effect account by 9.8, 6.3, and 54.0%, respectively. The effects of the ITZ elastic modulus and thickness, as well as the steel fiber length-to-diameter ratio on the SFRC creep, were analyzed via the proposed model. The grey relational analysis theory can characterize the correlation between related factors and various variations, so as to determine the key factors. Through this theory, it was revealed that the ITZ elastic modulus variation had the most significant effect on the SFRC creep.

Experimental study on the effect of corrosion on shear strength of fibre-reinforced concrete beams

In the present study, nineteen beam specimens with a dimension of 10 × 15 × 130 cm were prepared to investigate the shear behaviour of steel fibre-reinforced concrete (SFRC) beams exposed to corrosion. The tensile reinforcements of the specimens were subjected to 7% and 20% corrosion rates. Steel fibres in volume fractions of 0.8%, 1.2%, and 1.8% were added to concrete matrices. Six of the beam specimens were mixed with pre-corroded steel fibres at a corrosion level of 50% to study the hybrid effect of their corrosion and the longitudinal reinforcement on shear performance. The test results showed that adding the fibres improved the shear capacity, and reduced crack initiation and propagation due to corrosion, mode of failure, and deflection. The shear capacity of the non-corroded SFRC beams increased by about 68%, 72%, and 82% for the 0.8%, 1.2%, and 1.8% volume fractions of steel fibre, respectively, compared to RC beams without fibre. Also, the mode of failure changed from brittle shear failure to ductile flexure failure for SFRC beams. A 1.8% volumetric ratio of steel fibres was very useful in terms of enhancing shear behaviour. The corrosion in the tensile reinforcement of the beams reduced the shear strength by 6%–8% for the corrosion rates of 7% and 20%, respectively; however, the corrosion also reduced the maximum loading by 10%–22%. Furthermore, the corroded both steel fibres and corroded rebars reduced loading by 6%–37%. As a result, it was concluded that the steel fibres can enhance the performance of the beams for shear even in a harsh environment. Finally, the results of some models obtained from the literature to compute the shear strength of RC and SFRC beams with and without corrosion effect were compared with the experimental results of this study.

Effect of magnetic field exposure time on mechanical and microstructure properties of steel fiber-reinforced concrete (SFRC)

The present experimental study is an effort to investigate the effect of uniform magnetic field (UMF) exposure time on mechanical and microstructural behaviors of steel fiber-reinforced concrete (SFRC) with fiber volume fractions of 0.4, 0.7 and 1% by employing compressive and flexural strengths tests, and scanning electron microscopy (SEM) imaging. Following this, the brittleness index of SFRC specimens due to different exposure times was assessed. In addition, the ultrasonic test was employed to assess nondestructively the compressive strength of SFRC affected by the UMF for different times. For this purpose, ready-mixed SFRC specimens were exposed to the UMF of density 5000 Gauss, during the casting process, for three different time periods: 1, 2 and 3 min. The study also investigated the effect of UMF exposure direction on the compressive strength of SFRC specimens. Finally, an equation has been proposed to estimate flexural strength of SFRC exposed to the UMF based on compressive strength results. The obtained results demonstrated that the mechanical strength of SFRC increased as the UMF exposure time increased which is more obvious for specimens containing 0.7% steel fibers by volume of the concrete. Concerning this, compressive and flexural strengths of the specimens, exposed to the UMF for 3 min increased by about 21 and 27%, respectively. Furthermore, based on the SEM analysis, chemical reactions of cement hydration increased with increasing the UMF exposure time, leading to increasing bond between cement paste and steel fibers.

Behavior of Steel Fiber-Reinforced Concrete under Biaxial Stresses

Biaxial behavior of various types of concrete is essential to be considered in construction design because construction structures normally experience multiaxial stresses rather than uniaxial stress. Research on biaxial behavior of steel fiber-reinforced concrete (SFRC) has been conducted in the past decades. Most of the research, however, is only limited to biaxial compression, whereas information regarding biaxial tension and biaxial tensioncompression on SFRC is relatively scarce. This study presents a simple biaxial experimental setup to investigate the biaxial behavior of SFRC with 0.5, 1.0, and 1.5% steel fiber under biaxial tension and biaxial tension-compression. It is found that the smaller stress ratio enhanced the deformability and tensile capacity of SFRC under biaxial tension-compression, whereas the effect of stress ratio on biaxial tensile behavior of SFRC is negligible. The addition of steel fiber eventually enhanced the concrete strength by 15 to 41% under tension-compression compared with plain concrete.

Ductile‐to‐brittle transition in fibre‐reinforced concrete beams: Scale and fibre volume fraction effects

The mechanical response of fibre-reinforced brittle-matrix structural elements subjected to bending is discussed in the framework of fracture mechanics. By means of numerical simulations based on the bridged crack model, the flexural behaviour of steel fibre-reinforced concrete (FRC) beams has been investigated, taking into account pull-out or yielding bridging mechanism of the secondary phase. In both cases, the numerical results predict a transition of the global structural behaviour, which can range from ductile to catastrophic. This behaviour is governed by a dimensionless parameter, the brittleness number, NP, in which the effects of the structural size and the fibre volume fraction are included. An experimental campaign is carried out on FRC beams subjected to three-point bending tests, considering three different beam sizes and four different fibre contents. A comparison between experimental tests and numerical simulations shows that the bridging mechanism is due to the fibre slippage into the matrix, rather than the fibre plastic flow. The expected ductile-to-brittle transition is found for each beam scale, as predicted by NP. As a consequence, the minimum fibre volume fraction can be defined according to this model, providing an effective structural bearing capacity of FRC structural members.

Study of the Compression Behavior of Steel-Fiber Reinforced Concrete by Means of the Response Surface Methodology

The compression behavior of steel-fiber reinforced concrete (SFRC) has been addressed exhaustively in recent decades thereby highlighting a variety of differences with regard to the effect that the addition of fiber has on it. In this paper, a detailed study of the subject is developed for which a database has been created, which includes 197 tests performed on cylindrical concrete specimens with dimensions of 150 × 300 mm 2 (diameter × height). By means of the response surface methodology, we disclose the relationship that exists between the geometric parameters of the fiber (length, diameter, and aspect ratio), their amount (fraction in volume), and some matrix parameters (compression resistance and maximum size of coarse aggregate) with the different compression responses of the SFRC, which are strength, elastic modulus, critical deformation under maximum load, and the volumetric deformation work in the pre- and post-peak branch. Linear polynomial models are chosen to adjust each response with the defined factors, and said variables are studied in a dimensional and non-dimensional format. From the results obtained, it is verified how the inclusion of steel-fibers produces notable improvements in ductility and the energy absorption capacity of the concrete when significantly increasing the works of volumetric deformation in the pre- and post-peak branch with respect to the matrix without fibers. In addition, a new model is analyzed, which describes the stress–strain curve of the compression behavior of the SFRC based on the increase of ductility and energy absorption. This model is characterized by a softening branch subsequent to the peak load determined by means of the residual compressive strength, a parameter that corresponds to the value of the compressive stress associated with a strain equal to three times that of the peak of the curve, which is significantly dependent on the aspect ratio and fiber content.

Static and Dynamic Responses of a Reinforced Concrete Beam Strengthened with Steel and Polypropylene Fibers

Abstract This paper describes an experimental investigation on mono steel and polypropylene (PP) fiber-reinforced concrete beams. The main aim of this present study is to evaluate undamaged and damaged reinforced concrete (RC) beams incorporated with mono fibers such as steel and PP fibers under free-free constraints. In this experimental work, a total of nine RC beams were cast and analyzed in order to study the dynamic behavior as well as the static load behavior of steel fiber-reinforced concrete (SFRCs) and polypropylene fiber-reinforced concrete (PPFRCs). Damage to the SFRC and PPFRC beams was obtained by cracking the concrete for one of the beams in each set under four-point bending tests with different percentage variations of the damage levels such as 50%, 70% and 90% of the maximum ultimate load. The fundamental natural frequency and damping values obtained through the dynamic tests for the SFRC and PPFRC beams were compared with a control RC beam at each level of damage that had been acquired through static tests. The static experimental test results emphasize that the SFRC beam has attained a higher ultimate load compared with the control RC beam.

Effects of fiber orientation and content on the static and fatigue behavior of SFRC by using CT-Scan technology

The effects of the fiber orientation and content on the behavior of steel fiber-reinforced concrete (SFRC) under static and cyclic compressive loads are studied using the computed tomography (CT) technique, and the resistance mechanisms of the fibers are carefully observed. The results suggest that the intrinsic scatter in the fatigue life could be partially explained by the essential scatter in the fiber orientation and content. On the contrary, no relationship is observed between the intrinsic scatter in compressive strength and fiber orientation and content, which suggests that the compressive strength of the specimens is mainly due to their concrete matrix.

The influence of fibre spatial characteristics on the flexural performance of SFRC

Research has shown that the post-peak tensile strength behaviour of Steel Fibre-Reinforced Concrete (SFRC) elements is significantly affected by the distribution of fibres in the section. The pursuit towards the effective and optimal application of SFRC in practice necessitates a thorough understanding of the influence of fibre spatial distribution on composite performance. In this research, the influence of fibre length and volume content on the spatial distribution of fibres was investigated using a photometric image analysis technique. A unique approach was developed that utilises Voronoi diagrams as the geometric descriptor quantifying fibre spatial distribution. The resulting parameters characterised the sectional dispersion of fibres as well as the degree of clustering and were related to the flexural performance of notched beams tested under three-point loading. The findings of the study highlight the role of fibre length and volume content on the spatial distribution of fibres and it is revealed that the sectional uniformity, inter-batch spatial variability, and degree of clustering are dependent on the number of fibres in the cross section. Furthermore, the results demonstrated the considerable influence of fibre distribution on the flexural performance of SFRC. It was concluded that the variability in flexural strength reduced as the variation in fibre spatial distribution reduced and that extensive clustering had an adverse effect on the effective resistance provided by fibres.

A Study on Elastic Deformation Behavior of Steel Fiber-Reinforced Concrete for Pavements

The present study discusses the experimental investigation of steel fiber-reinforced concrete slabs on ground under wheel load with the objective of understanding the stress behavior when subjected to central and edge wheel loading. The steel fiber-reinforced fly ash concrete slabs of 900 mm × 900 mm, 150 mm thickness were investigated in this study. Strain gauges and data acquisition system were used to measure the strains at the center and the edge of the slab under the action of the load. The load versus strain relationship under central and edge loading for reference concrete and steel fiber fly ash concrete showed a linear variation even up to the pressure of 2.5 MPa, which is much beyond the conventional tyre inflation pressure of 0.8 MPa. The load versus strain graphs clearly signify the higher modulus of elasticity of fly ash steel fiber-reinforced concrete. The stresses were calculated using IITRIGID software and ANSYS software and were found matching significantly. The value of modulus of elasticity of fly ash steel fiber-reinforced concrete (FS) using ANSYS model for experimental values of load and strains measured was approximated to 34,000 N/mm2 and was found to closely match with the experimentally obtained modulus of elasticity. No significant effect of Poisson’s ratio of concrete on load–strain characteristics was observed within the range 0.15–0.2 of concrete.

Fiber-reinforced concrete containing ultra high-strength micro steel fibers under active confinement

This paper presents an experimental study on the compressive behavior of steel fiber-reinforced concrete (SFRC) under active confining pressure. Four different SFRC mixes containing ultra high-strength micro steel fibers at two volume fractions of 1% and 2% were prepared to produce concretes with two different target compressive strengths of 50 and 100 MPa. The active confining pressure was applied on SFRC using a Hoek cell at different confinement levels of 5, 10, 15, and 25 MPa. The effects of confining pressure and steel fiber volume fraction on the compressive behavior of concrete were examined through the axial compression tests on unconfined and actively confined SFRCs. The results show that the axial strength and peak axial strain of SFRCs increase with an increase in the fiber volume fraction. The fiber volume fraction also affects the post-peak branch trend of the axial stress-strain relationships of SFRCs under a given confinement level. SFRCs with a higher volume fraction exhibit more shallow post-peak branches than those of SFRCs with a lower volume fraction. The results also show that the axial strain of SFRC at a given lateral strain increases with an increase in the volume fraction, indicating a reduced rate of dilation of SFRCs at a higher volume fraction. These promising findings point to the great potential of the use of ultra high-strength micro steel fibers in the development of high performance composite structural members in applications where the concrete will be subjected to lateral confinement.

Different properties of steel fibres reinforced concrete review article

Properties of fibre reinforced concrete (FRC) are mainly influenced by type and amount of fibres. Practically, fibre properties are defined by the fibre producers. The mechanical behaviour of fibre reinforced concrete depends largely on the interactions between the fibres and the brittle concrete matrix: physical and chemical adhesion; friction; and mechanical anchorage induced by complex fibre geometry or by deformations or other treatments on the fibre surface. The mechanical performance of steel fibre reinforced concrete (SFRC) is also highly influenced by the fibre dispersion, since the effectiveness of fibre reinforcement depends on the orientation and arrangement of the fibres within the cement matrix, in which, short and randomly distributed steel fibres are often used for concrete reinforcement since they offer resistance to crack initiation and, mainly, to crack propagation. In present paper we intended to give an overview of different parameters and their influence on the behaviour of SFRC.

A study of strain-rate effect and fiber reinforcement effect on dynamic behavior of steel fiber-reinforced concrete

This paper presents an experimental study on uniaxial mechanical properties of steel fiber-reinforced concrete (SFRC) subjected to high strain-rate compressive loading. SFRC specimens of 6 different steel fiber volume fractions (0.0%, 0.75%, 1.5%, 3.0%, 4.5% and 6.0%) are fabricated and tested using a 75-mm-diameter split Hopkinson pressure bar (SHPB). Wave-shapers are investigated to ensure that two basic assumptions of SHPB hold true and that constant strain-rate is maintained within SFRC specimens. Based on acquired dynamic stress–strain relations, dynamic strength increase factor, fiber reinforcement factor, critical strain, and energy absorption are studied versus both strain-rate and fiber volume fraction. That provides an insight into strain-rate effect and fiber reinforcement effect on dynamic behavior of plain concrete and SFRC. The mechanisms underlying strain-rate effect and fiber reinforcement effect are discussed.

Mechanical Behavior of Steel Fiber-Reinforced Concrete Beams Bonded with External Carbon Fiber Sheets.

This study investigates the mechanical behavior of steel fiber-reinforced concrete (SFRC) beams internally reinforced with steel bars and externally bonded with carbon fiber-reinforced polymer (CFRP) sheets fixed by adhesive and hybrid jointing techniques. In particular, attention is paid to the load resistance and failure modes of composite beams. The steel fibers were used to avoiding the rip-off failure of the concrete cover. The CFRP sheets were fixed to the concrete surface by epoxy adhesive as well as combined with various configurations of small-diameter steel pins for mechanical fastening to form a hybrid connection. Such hybrid jointing techniques were found to be particularly advantageous in avoiding brittle debonding failure, by promoting progressive failure within the hybrid joints. The use of CFRP sheets was also effective in suppressing the localization of the discrete cracks. The development of the crack pattern was monitored using the digital image correlation method. As revealed from the image analyses, with an appropriate layout of the steel pins, brittle failure of the concrete-carbon fiber interface could be effectively prevented. Inverse analysis of the moment-curvature diagrams was conducted, and it was found that a simplified tension-stiffening model with a constant residual stress level at 90% of the strength of the SFRC is adequate for numerically simulating the deformation behavior of beams up to the debonding of the CFRP sheets.